This application is a 371 of PCT/JP98/03139 filed Jul. 14, 1998.
The present invention relates to a glycol dispersion of an inorganic powder and production method thereof, and a polyester composition containing said dispersion. More particularly, the present invention relates to a glycol dispersion of an inorganic powder and production method thereof, and a polyester composition containing said dispersion, which attain simplification of production steps, reduction of transportation cost and prevention of breakage of inorganic particles in a method for dispersing an inorganic powder in glycol such as ethylene glycol in an attempt to improve a coefficient of friction and hue of a polyester, and to impart opacity and micropores to a polyester, which is for use in film or fiber, in particular.
Nowadays, polyester produced industrially, especially polyethyleneterephthalate has excellent physical and chemical characteristics and thus has been widely used as fiber, film and other molded articles. In such a polyester composition, it has been conventionally carried out to cause fine particles to be contained in polyester in order to improve a coefficient of friction and hue of polyester and to impart opacity and micropores to polyester.
For example, in the case of reducing a coefficient of friction, it is known that since polyester is inferior in slipperiness in molding and processing steps as well as in handling of products, troubles such as deterioration in workability and commercial value arise, in spite of its excellent characteristics. Most of such causes come from a high coefficient of friction of polyester itself. As a measure to these troubles, many methods are proposed and put into practice which allow fine particles to be contained in polyester to thus impart appropriate uneveness to the surface of a molded article so that surface smoothness of the molded article is improved.
As means of improving the surface characteristics of polyester, the following two methods have been known:
(1) a method for separating out a part or whole of a catalyst or the like used for the synthesis of polyester in the reaction process (internal particle separating-out method), and
(2) a method for adding fine particles such as calcium carbonate and silicon dioxide in the course of or after polymerization (external particle adding method).
However, the internal particle separating-out method (1) has a drawback of having difficulty in controlling the amount and size of particles and in preventing the formation of coarse particles because in this method particles are to be formed during reaction, though the affinity between polyester and particles is somewhat good, for such particles consist of a metallic salt of a polyester component.
The external particle adding method (2), which consists in adding fine particles of an inorganic compound insoluble in and inert to polyester such as titanium dioxide, silica, talc, kaolin and calcium carbonate during or after polymerization, is superior to the method (1) described above with regard to the improvement of sliding property, if the particle size and the amount of addition of the inorganic compound are properly selected and coarse particles are removed by classification or the like in advance.
Also, for the improvement of dispersibility in polyester of such fine particles of an inorganic compound there is proposed a method of preparing a glycol slurry of fine particles of an inorganic compound and adding it in the process of the polyester manufacture, but there is something to be desired about the dispersibility as well as long-term dispersion stability of such fine particles of an inorganic compound in glycol, hence, when the glycol with such fine particles of an inorganic compound suspended therein is stored for a long period of time, there are problems that such fine particles of an inorganic compound precipitate to form hard cakes which are difficult to redisperse, and that fine particles of such inorganic compound agglomerate in glycol or in the course of manufacture of polyester. The presence of agglomerated coarse particles in polyester causes yarn breakage in the spinning process, formation of the so-called xe2x80x9cfish eyexe2x80x9d and, in particular, drop-out or lowering of S/N ratio when it is used for the manufacture of film for magnetic tape.
As the particles having a high dispersibility used such uses, vaterite calcium carbonate, spherical silica prepared by a sol-gel method, calcite cubic calcium carbonate may be exemplified. Those are produced by a high technique so that individual particles may be present without aggregation. Those are usually prepared in water or alcohol and it is necessary to prepare a slurry of the monodispersed particles and glycol by substituting water or alcohol with glycol while maintaining a high dispersion. For this purpose, a vacuum distiller such as an evaporator is used but this method is high expensive. Moreover, even when the glycol slurry prepared in this way is transported to a place where polyester is produced, or even when a slurry containing water or methanol is transported to a production place of polyester and distilled therein, there is not a bit of difference between the two in that the transportation is made in the form of slurry so that a decrease in transportation efficiency and an increase in transportation cost are not avoidable.
In order to solve those problems, it is considered to obtain a powder by drying the particles monodispersed in water or methanol by the use of a dryer such as a spray dryer, and to mix the powder with glycol to thus prepare a glycol slurry. However, the monodispersed particles, when dried, form aggregates and therefore the monodispersed particles prepared in this method are not redispersed in glycol in good dispersion state of the original particles.
Moreover, Japanese Patent Examined Publication No. 2-48174 proposes a method for obtaining good dispersibility by wet-pulverizing in glycol a precipitated calcium carbonate having the specific dispersibility and particle size under the specific conditions. Although this method is said to be good in uses in which ununiformity of the particle shape in glycol dispersion is not problematic, it is not suitable for spherical or cubic monodisperse calcium carbonate having the uniform shape and particle size.
Although, for example, a glycol dispersion having a good dispersibility is obtained if spherical calcium carbonate or silica obtained by a spray dryer is used in the form of powder as a wet-pulverizing material and its glycol slurry is wet-pulverized according to the method described in the above publication, a cost is not only increased since the wet-pulverizing step is added, but the shape is irregular due to the pulverization and the original shape is lost. In addition, unintended fine particles occasionally generate due to the pulverization and they reaggregate to form coarse particles in the production step of polyester, which deteriorates the physical properties of the composition. Furthermore, in the method described in the publication, fragments of a medium such as glass used for the pulverization are mingled into the pulverized matters. The fragments are usually coarse particles of 10 to 100 xcexcm and thus this method is not suitable for film of polyester or the like.
As stated above, it is difficult to prepare a glycol dispersion by dispersing an inorganic powder in glycol while maintaining its shape and particle size before drying or in the initial state. Therefore, it is impossible to transport inorganic particles in the form of powder for the purpose of reducing a transportation cost and for this reason, the transportation in the form of slurry is forced, otherwise, even when the transportation in the form of powder is possible, it is very expensive to prepare a glycol slurry of satisfactory dispersion from this powder.
In light of the foregoing situation, the present invention provides a method for producing a glycol dispersion which is not only capable of a drastic simplification in the production steps and a reduction in cost by omitting the use of an distillation apparatus for substituting a solvent such as water and methanol with glycol, requiring neither transportation of water, methanol or glycol slurry nor a wet-pulverization step, but capable of dispersing an inorganic powder in glycol with maintaining its particle shape and particle size before drying or in the initial state, and further provides a polyester composition containing the glycol dispersion of the inorganic powder uniformly dispersed in glycol.
The present inventors have made an extensive series of studies in an attempt to solve the above problems and have found out that a glycol dispersion is obtained which not only has an excellent dispersibility, but realizes a reduction in transportation cost, simplification of production steps and the maintenance of the particle shape and size, by using an inorganic powder surface-treated with a dispersant having a specific range of solubility and adding a small amount of water and /or methanol adjusted in an amount and a concentration so as to satisfy the specific conditions, and that a polyester composition having an excellent performance is provided by using the glycol dispersion in films, fibers and molded articles, thus completed the present invention.
The present invention is, in a first aspect, to provide a glycol dispersion of an inorganic powder which comprises glycol and an inorganic powder dispersed therein, said inorganic powder being surface-treated with a dispersant having a solubility of not less than 5 (g/100 g-water) in water of 20xc2x0 C., and which contains water and/or methanol in a range to satisfy the following equations (1) to (3):
1xe2x89xa6Axe2x89xa620/txe2x80x83xe2x80x83(1)
0.5xe2x89xa6Bxe2x89xa610xe2x80x83xe2x80x83(2)
5xe2x89xa6Cxe2x80x83xe2x80x83(3)
wherein
A: % by weight of water and/or methanol based on the inorganic powder,
t: % by weight of the dispersant based on the inorganic powder,
B: % by weight of water and/or methanol in the glycol dispersion,
C: % by weight of the inorganic powder in the glycol dispersion.
The present invention is, in a second aspect, to provide a method for producing a glycol dispersion of an inorganic powder which comprises the following steps of:
surface-treating an inorganic powder with a dispersant having a solubility of not less than 5 (g/100 g-water) in water of 20xc2x0 C., and
dispersing the surface-treated inorganic powder in glycol together with water and/or methanol so as to satisfy the following equations (1) to (3):
1xe2x89xa6Axe2x89xa620/txe2x80x83xe2x80x83(1)
0.5xe2x89xa6Bxe2x89xa610xe2x80x83xe2x80x83(2)
5xe2x89xa6Cxe2x80x83xe2x80x83(3)
wherein
A: % by weight of water and/or methanol based on the inorganic powder,
t: % by weight of the dispersant based on the inorganic powder,
B: % by weight of water and/or methanol in the glycol dispersion,
C: % by weight of the inorganic powder in the glycol dispersion.
The present invention is, in a third aspect, to provide a polyester composition containing the above-mentioned glycol dispersion of an inorganic powder.